The influence of water level on macrophyte growth and trophic interactions in eutrophic Mediterranean shallow lakes: a mesocosm experiment with and without fish

1. Water‐level fluctuations are typical of lakes located in the semi‐arid Mediterranean region, which is characterised by warm rainy winters and hot dry summers. Ongoing climate change may exacerbate fluctuations and lead to more severe episodes of drought, so information on the effects of water level on the functioning of lake ecosystems in such regions is crucial. 2. In eutrophic Lake Eymir, Turkey, we conducted a 4‐month (summer) field experiment using cylindrical 0.8‐m‐ (low‐water‐level) and 1.6‐m‐deep (high‐water‐level) mesocosms (kept open to the sediment and atmosphere). Fish (tench, Tinca tinca, and bleak, Alburnus escherichii) were added to half of the mesocosms, while the rest were kept fishless. Ten shoots of Potamogeton pectinatus were transplanted to each mesocosm. 3. Sampling for physicochemical variables, chlorophyll a (chl‐a), zooplankton and per cent plant volume inhabited (PVI%) by macrophytes was conducted weekly during the first 5 weeks, and subsequently biweekly. Macrophytes were harvested on the last sampling date. During the course of the experiment, the water level decreased by 0.41 ± 0.06 m. 4. Throughout the experiment, fish affected zooplankton abundance (?), nutrient concentrations (+), chl‐a (+) and water clarity (?) most strongly in the low‐water‐level mesocosms and the zooplankton community shifted towards dominance of small‐sized forms. The fishless mesocosms had a higher zooplankton/phytoplankton ratio, suggesting higher grazing. 5. Greatest macrophyte growth was observed in the low‐water‐level fishless mesocosms. However, despite high nutrient concentrations and low water clarity, macrophytes were also abundant in the fish mesocosms and particularly increased following a water‐level decrease from midsummer onwards. Macrophyte growth was poor in the high‐water‐level mesocosms, even in the fishless ones with high water clarity. This was ascribed to extensive periphyton development reducing light availability for the macrophytes. 6. Our results indicate that a reduction in water level during summer may help maintain the growth of macrophytes in Mediterranean eutrophic shallow lakes, despite a strong negative effect of fish predation on water clarity. It is therefore probable that an expected negative effect of global climate change on water clarity because of eutrophication and enhanced top‐down control of fish may be, at least partly, counteracted by reduced water level, provided that physical disturbance is not severe.     

Gut microbiome composition and function in experimental colitis during active disease and treatment-induced remission

Dysregulated immune responses to gut microbes are central to inflammatory bowel disease (IBD), and gut microbial activity can fuel chronic inflammation. Examining how IBD-directed therapies influence gut microbiomes may identify microbial community features integral to mitigating disease and maintaining health. However, IBD patients often receive multiple treatments during disease flares, confounding such analyses. Preclinical models of IBD with well-defined disease courses and opportunities for controlled treatment exposures provide a valuable solution. Here, we surveyed the gut microbiome of the T-bet^−/− Rag2^−/− mouse model of colitis during active disease and treatment-induced remission. Microbial features modified among these conditions included altered potential for carbohydrate and energy metabolism and bacterial pathogenesis, specifically cell motility and signal transduction pathways. We also observed an increased capacity for xenobiotics metabolism, including benzoate degradation, a pathway linking host adrenergic stress with enhanced bacterial virulence, and found decreased levels of fecal dopamine in active colitis. When transferred to gnotobiotic mice, gut microbiomes from mice with active disease versus treatment-induced remission elicited varying degrees of colitis. Thus, our study provides insight into specific microbial clades and pathways associated with health, active disease and treatment interventions in a mouse model of colitis.     

Biomarkers for oxidative stress in acute lung injury induced in rabbits submitted to different strategies of mechanical ventilation

Oxidative damage has been said to play an important role in pulmonary injury, which is associated with the development and progression of acute respiratory distress syndrome (ARDS). We aimed to identify biomarkers to determine the oxidative stress in an animal model of acute lung injury (ALI) using two different strategies of mechanical ventilation. Rabbits were ventilated using either conventional mechanical ventilation (CMV) or high-frequency oscillatory ventilation (HFOV). Lung injury was induced by tracheal saline infusion (30 ml/kg, 38°C). In addition, five healthy rabbits were studied for oxidative stress. Isolated lymphocytes from peripheral blood and lung tissue samples were analyzed by alkaline single cell gel electrophoresis (comet assay) to determine DNA damage. Total antioxidant performance (TAP) assay was applied to measure overall antioxidant performance in plasma and lung tissue. HFOV rabbits had similar results to healthy animals, showing significantly higher antioxidant performance and lower DNA damage compared with CMV in lung tissue and plasma. Total antioxidant performance showed a significant positive correlation (r = 0.58; P = 0.0006) in plasma and lung tissue. In addition, comet assay presented a significant positive correlation (r = 0.66; P = 0.007) between cells recovered from target tissue and peripheral blood. Moreover, antioxidant performance was significantly and negatively correlated with DNA damage (r = -0.50; P = 0.002) in lung tissue. This study indicates that both TAP and comet assay identify increased oxidative stress in CMV rabbits compared with HFOV. Antioxidant performance analyzed by TAP and oxidative DNA damage by comet assay, both in plasma, reflects oxidative stress in the target tissue, which warrants further studies in humans.     

Endothelin-1 and endothelin receptors in the basilar artery of the capybara

Little is known about cerebral vasculature of capybara, which seems may serve as a natural model of studying changes in cerebral circulation due to internal carotid artery atrophy at animal sexual maturation. This is the first study of the light- and electron-immunocytochemical localisation of endothelin-1 (ET-1) and ET_A and ET_B endothelin receptors in the basilar artery of capybaras (6 to 12-month-old females and males) using an ExtrAvidin detection method. All animals examined showed similar patterns of immunoreactivity. Immunoreactivity for ET-1 was detected in the endothelium and adventitial fibroblasts, whilst immunoreactivity for ET_A and ET_B receptors was present in the endothelium, vascular smooth muscle, perivascular nerves and fibroblasts. In endothelial cells immunoreactivity to ET-1 was pronounced in the cytoplasm or on the granular endoplasmic reticulum. Similar patterns of immunolabelling were observed for ET_A and ET_B receptors, though cytoplasmic location of clusters of immunoprecipitate seems dominant. These results suggest that the endothelin system is present throughout the wall of the basilar artery of capybara.     

Structural analysis of the anaphase-promoting complex reveals multiple active sites and insights into polyubiquitylation

The anaphase-promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase composed of approximately 13 distinct subunits required for progression through meiosis, mitosis, and the G1 phase of the cell cycle. Despite its central role in these processes, information concerning its composition and structure is limited. Here, we determined the structure of yeast APC/C by cryo-electron microscopy (cryo-EM). Docking of tetratricopeptide repeat (TPR)-containing subunits indicates that they likely form a scaffold-like outer shell, mediating assembly of the complex and providing potential binding sites for regulators and substrates. Quantitative determination of subunit stoichiometry indicates multiple copies of specific subunits, consistent with a total APC/C mass of approximately 1.7 MDa. Moreover, yeast APC/C forms both monomeric and dimeric species. Dimeric APC/C is a more active E3 ligase than the monomer, with greatly enhanced processivity. Our data suggest that multimerisation and/or the presence of multiple active sites facilitates the APC/C's ability to elongate polyubiquitin chains.     

Nucleotide sequence divergence in the A+T-rich region of mitochondrial DNA in Drosophila simulans and Drosophila mauritiana

We have determined the nucleotide sequences of two regions within the A+T-rich region of mitochondrial DNA (mtDNA) in the siIII type of Drosophila simulans and the maI type of D. mauritiana. The sequences of the two regions in siIII and maI are almost identical. The sequences include elements corresponding to the type I and type II repeats elements and the T-stretches as reported in D. melanogaster; an approximately 340-bp region (A region) adjacent to the tRNA(Ile) gene includes a part of the type II repeat element, and an approximately 440- bp region (B region) includes a central portion of the A+T-rich region between the type I and type II repeat arrays. Each sequence of the two species was compared with those of D. melanogaster and D. yakuba. The sequences of the A region are relatively well conserved among the four species. The alignment of the two sequences of the B region with those of D. melanogaster and D. yakuba requires numerous insertions/deletions. For both regions, nucleotide differences between D. simulans or D. mauritiana and D. melanogaster are similar to those between the two and D. yakuba. The tendency is obvious in a subregion within the type II repeat element in the A region. These findings suggest that the rate of nucleotide substitution in the subregion is accelerated in the lineage leading to D. melanogaster. Loss of functional constraint in the stem-loop-forming sequence is proposed for this acceleration.      

Organisation de type tétracoralliaire des rides septales de Palaeacis (Cnidaria, Carbonifére)

Plusquellec, Y., Lafuste, J. & Webb, G. E. 1990 10 15: Organisation de type tétracoralliaire des rides septales de Palaeacis (Cnidaria, Carbonifére). Lethaia, Vol. 23, pp. 385–397. Oslo. ISSN 0024–1164. Precedemment signalée chez Kerforneidictyum (Pleurodictyforme dévonien), la rare disposition des rides septales suivant un mode tétracoralliaire est décrite chez un Palaeack sp. du Viséen d'Algérie et chez P. cuneiformis subsp. A du Viseen d'Australie. Chez Palaeacis sp. sont mises en evidence une ride septale cardinale forte en position externe opposée à une ride antipode déterminant un plan de symétrie bilatérale; de part et d'autre une zone systématiquement confuse marque l'emplacement des rides alaires. La reconnaissance des périantipodes prête à discussion et ce secteur présente une originalité certaine par rapport à celui des Tétracoralliaires. Chez P. cuneiformis subsp. A, une coupe transversale montre la présence de quatre rides proéminentes qui fusionnent dans I'axe du corallite et I'existence d'une symétrie bilatérale. La position systématique du genre Palaeacis est discutée: son attribution aux Tétracoralliaires est exclue, ancun caractére n'est incompatible avec le statut de Tabulé, la création d'une unité taxon-omique nouvelle regroupant Palaeacis, Trachypsammia et les Pleurodictyformes est envisageable mais actuellement prématurée. ? Palaeacis, Tabulata, Rugosa, rides septales, systématique, relations deparenré, Viséen. The tetracoral pattern of septal ridges described in Kerforneidictyum (Devonian Pleurodictyum-like coral) is scar'ce in the Tabulata, but has been found in Palaeacis sp. from the Visean of Algeria and in P. cuneiformis subsp. A from the Visean of Australia. Palaeacis sp. shows a strong cardinal septal ridge in peripheral position, just opposite the counter ridge. thus creating a plane of bilateral symmetry: an area on both sides. which is always blurred, indicates the position of the alar ridges. counter-lateral ridges are not easily identified and yield differing interpretation. Compared with the Rugosa this area presents distinctive features. In P. cuneiformis subsp. A, a transverse section exhibits four well-developed septal ridges that coalesce in the axis of the corallite with obvious bilateral symmetry. The systematic position of the genus Palaeacis is questioned: Rugosa it is not; it may belong to Tabulata: however, erecting a new higher taxon for Palaeacis, Trachypsammia and other Pleurodictyum-like corals is premature at our present state of knowledge. ? Palaeacis, Tabulata, Rugosa, septal ridges, systematic. affinities, Visean.     

Daily malate fluctuations in Sedum dasyphyllum L.

Abstract

Sedum dasyphyllum L. leaves of well-watered plants kept outdoors and under controlled conditions show diurnal malic acid fluctuations. In well-watered plants growing outdoors the malate accumulation undergoes seasonal variations and seems to be inhibited by short photoperiod and/or by low temperature. The seasonal variations of CAM activity correspond to seasonal variations of mesophyll succulence. Water stress markedly depressed CAM activity. In fact, plants of S. dasyphyllum show, under controlled conditions, a decrease of malate accumulation as relative water content decreases. Recovery from water stress is fairly slow. Water potential quickly increases during rewatering and exceeds the original value after few days, suggesting a consumption of osmotic compounds during the water stress period.     

Substructural specificity and polyvalent carbohydrate recognition by the Entamoeba histolytica and rat hepatic N- acetylgalactosamine/galactose lectins

Both the Entamoeba histolytica lectin, a virulence factor for the causative agent of amebiasis, and the mammalian hepatic lectin bind to N-acetylgalactosamine (GalNAc) and galactose (Gal) nonreducing termini on oligosaccharides, with preference for GalNAc. Polyvalent GalNAc- derivatized neoglycoproteins have >1000-fold enhanced binding affinity for both lectins (Adler,P., Wood,S.J., Lee,Y.C., Lee,R.T., Petri,W.A.,Jr. and Schnaar,R.L.,1995, J. Biol. Chem ., 270, 5164-5171). Substructural specificity studies revealed that the 3-OH and 4-OH groups of GalNAc were required for binding to both lectins, whereas only the E.histolytica lectin required the 6-OH group. Whereas GalNAc binds with 4-fold lower affinity to the E.histolytica lectin than to the mammalian hepatic lectin, galactosamine and N-benzoyl galactosamine bind with higher affinity to the E. histolytica lectin. Therefore, a synthetic scheme for converting polyamine carriers to poly-N-acyl galactosamine derivatives (linked through the galactosamine primary amino group) was developed to test whether such ligands would bind the E.histolytica lectin with high specificity and high affinity. Contrary to expectations, polyvalent derivatives including GalN6lys5, GalN4desmosine, GalN4StarburstTMdendrimer, and GalN8StarburstTMdendrimer demonstrated highly enhanced binding to the mammalian hepatic lectin but little or no enhancement of binding to the E.histolytica lectin. We propose that the mammalian hepatic lectin binds with greatest affinity to GalNAc "miniclusters," which mimic branched termini of N-linked oligosaccharides, whereas the E.histolytica lectin binds most effectively to "maxiclusters," which may mimic more widely spaced GalNAc residues on intestinal mucins.